1. Field of the Invention
The present invention is broadly concerned with improved extrusion assemblies used for the processing of animal feeds or human foods and giving enhanced Specific Mechanical Energy values as compared with conventional extruder designs. More particularly, the invention is concerned with such extrusion assemblies wherein the extruder barrel is equipped with a mid-barrel valve assembly permitting selective, variable flow of material therethrough, together with a disrupting/homogenizing screw section upstream of the valve assembly. In further preferred aspects of the invention an atmospheric vent is provided downstream of the variable valve assembly.
2. Description of the Prior Art
Extrusion systems are commonly used in the production of human foods and animal feeds. Broadly speaking, there are two types of extrusion systems, namely single screw and twin screw systems. As the names imply, single screw extruders include an elongated barrel with only a single, elongated, helically flighted, axially rotatable screw assembly therein. In contrast, twin screw extruders have specially configured barrels with a pair of juxtaposed, helically flighted, axially rotatable and intercalated screw assemblies. It is also quite common to employ a preconditioning device upstream of a single or twin screw extruder, which serves to at least partially cook the starting materials and gelatinized the starch-bearing components thereof. Normally, higher levels of cook and gelatinization are desired inasmuch as this lessens cooking requirements in the downstream extruder, leading to higher quality products and increased throughputs.
A large number of specific extruder configurations have been proposed in the past in an effort to maximize Specific Mechanical Energy (SME) and cook levels without a concomitant increase in energy input by way of thermal energy. To this end, it has been known to use steamlocks along the length of the extruder screw(s) as well as variable valving systems providing both fixed and variable material flow restrictions. While such expedients are common, they have not provided the higher SME and cook values desired by extrusion processors.
There is accordingly a need in the art for improved extrusion assemblies capable of enhancing SME and cook values during the processing of animal feeds or human foods, without the need for significantly increased energy inputs.